Motor control system



Aprll 4, 1961 W RHINE 2,978,130

MOTOR CONTROL SYSTEM Filed sept. 2e, 195? 4 sheets-sheet 1 lll will

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April 4, 1961 w. c. R'HINE 2,978,130

MOTOR CONTROL SYSTEM Filed Sept. 26, 1957 4 Sheets-Sheet 2 Ni, si

April 4, 1961 w. c. RHINE MOTOR CONTROL SYSTEM 4 Sheets-Sheet 3 FiledSept. 26, 1957 2m# :SENT m3 m51 Y2 J|| 3 3 .y Q3 l .wmv v3 3- n Q M w. un n EL E: Hx". 3. m5 23. of TS.: n L 33j n 8-, don E nW( o5. inl u nV 23.51 3 Tau H UAT :am w $.10; olhm. .H U m .s 2m .T |I. n $3 auf RIJ EWI)i April 4, 1961 w. c. RHINE MOTOR CONTROL SYSTEM 4 Sheets-Sheet 4 FiledSept. 26, 1957 0 Quunm Qm mm nemen mr. S 80% speso s nemen United StatesPatent O MOTOR CONTROL SYSTEM William C. Rhine, Menomonee Falls, Wis.,assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation ofDelaware Filed Sept. 26, 1957, Ser. No. 686,482

14 Claims. (Cl. 214-656) This invention relates to improvements in motorcontrol systems. n

While not limited thereto, the invention is especially applicable tocontrollers for two-motor bucket hoists employed in unloading towers andthe like.

It has been found desirable to provide an improved electrical motorcontrol system employing a single master control for operating both theholding and closing motors and a clutch. It is also desirable toincrease the bucket speed over that of prior systems.

Accordingly, an object of the invention is to prov1de improved meansyaffording the aforementioned and other improved results.

A specific object of the invention is to provide an improved controlsystem for automatically affording irnproved matched speed operation ofa plurality of electrical motors.

A more specific object of the invention is to provide improved controlmeans for controlling clutching means between such motors to improve theoperation of the latter.

Another specific object of the invention is to provide an improvedcontrol system for automatically alfording matched speed operation of aplurality of electrical motors throughout all lowering speed points of ahoisting machine.

Another object of the invention is to provide improved selectivelycontrollable means affording hoist motor lowering speeds substantiallyabove the synchronous speed thereof.

A further object of the invention is to provide an improved bucket hoistcontrol system which is simple in construction while affording allrequired operations with minimum manipulation by the operator.

Other objects and advantages of the invention will hereinafter appear.

While the apparatus hereinafter described is effectively adapted tofulfill the objects stated, it is to be understood that I do not intendto conne my invention to the particular preferred embodiment of motorcontrol system disclosed, inasmuch as it is susceptible of variousmodifications without departing from the scope of the appended claims.

In the drawings:

Fig. l is a schematic illustration of a motor-drive mechanismconstructed in accordance with the present invention;

Fig. 2 diagrammatically shows power circuits and speed control networksfor the motors of Fig. l;

Figs. 3A and 3B diagram-matically show a master control system operablein conjunction with Fig. 2 for controlling the mechanism of Fig. l;

Fig. 4 graphically illustrates bucket speed characteristics of theinvention;

Fig. 5 is a graph showing speed-torque curves for the motors of Fig. l;and

Fig. 6 graphically depicts bucket speed-checking characteristics whenlowering an open bucket.

The motor-drive mechanism shown in Fig. l is enlployed to operate theholding and closing lines of a twomotor bucket hoist for unloadingtowers. A hold motor HM and a close motor CM are connected through theirdriven shafts 2 and 4, respectively, to opposite sides of a normallydisengaged clutch CW preferably of the electromagnetic type. Hold motorHM is further connected through shaft 2 to a brake HB and a gear box 6and through the latter to a drum 8 fo-r winding and unwinding theholding lines. Similarly, close motor CM is connected through shaft 4 toa brake CB and a gear box 10 and through the latter to a drum l2 forwinding and unwinding the closing lines. Hold motor brake HB and closemotor brake CB are preferably of the spring-applied type having anelectro-responsive Winding for disengaging the same as hereinafter morefully described.

As shown in Fig. 2, hold motor HM and close motor CM, preferably of thethree-phase slip-ring type, are connectable in parallel to power supplylines L1, L2 and L3, the latter being connectable through the usualonoif switches to a three-phase power supply source (not shown).

The stator or primary winding of motor HM is c011- nectable to supplylines L1-3 for forward or reverse energization through normally opencontacts HH2-4 or normally open contacts HL2-4- of a hoisting contactorHH and a lowering contactor HL, respectively. Contactor HH furthercomprises an operating coil HHI and contacts HHS-10 also shown in Figs.SA-B, while contactor HL has an operating coil HLl and additionalcontacts ELS-6 also shown in Fig. 3A.

The rotor or secondary winding of motor HM is connected to a resistancenetwork having nine groups of resistors lil-9, each such groupcomprising three resistors in series connection, respectively, withcorresponding resistors of the other groups in the three phases of therotor winding. Com-mutating contactors HSL, H2L, HlL, HP, HIA, HZA, H3Aand H4A having pairs of normally open contacts H3L2-3, HZLZ-S, H1L2-3,HP2-3, H1A2-3, H2A23, H3A2-3, and H4A2-3 are provided for etectivelyshunting resistor groups Rl-S, respectively, out of circuit ashereinafter described. The aforesaid commutating contactors are providedwith operating coils HSLI, H2L1, HlLl, HPl, H1A1, HZAI, H3Al and H4Al,respectively, while contacter HP is additionally provided with contactsHP4-6, contactor HlA with contacts H1A4-5, contacter HZA with contactsHZA-t-S and contactor H3A with contacts H3A4-5, also shown in Fig. 3B.

A full-wave rectifier bridge RT 1 for supplying voltage relays IVR andZVR is connected at its input terminals to the junctions of the rotorwinding and resistor group R9 for energization by one phase of the motorsecondary voltage, operating coils 1VR1 and 2VR1 of the voltage relaysbeing connected in parallel to the positive and negative outputterminals of the rectier bridge. Relay IVR is provided withnormally-open contacts 1VR2 while relay ZVR is provided withnormally-closed contacts ZVRZ, also shown in Fig. 3A, for operation ashereinafter described.

The stator winding of motor CM is connectable to supply lines L1-3 forforward or reverse energization through normally open contacts CH2-4 ornormally open contacts CL2-4 of a hoisting contactor CH and a loweringcontacter CL, respectively. Contactor CH further comprises an operatingcoil CHI and contacts CHS-9 also shown in Figs. 3A-B, while contacter CLhas an operating coil CL1 and additional contacts CLS-7 also shown inFig. 3A.

AThe rotor winding ofV motor CM is connected Ato a resistance networkhaving eight groups of resistors R11- 18, each suchgroup comprisingthree resistors in series connection, respectively, with correspondingresistors of the other groups in the three phases of the rotor winding.Commutating contactors C2L, C1L, CP, C1A, C2A, C3A and C4A having pairsof normally open contacts C2L2 3, CILE-3, CP2-3, C1A2-3, C2A2-3, VC3A2-3and C4A2-3 are provided for effectively shunting resistor groups R11-17,respectively, out of circuit as hereinafter described. The aforesaidcommutating contactors are provided with operating coils C2L1, C1L1,CP1, C1A1, C2A1, C3A1, and C4A1, respectively, while contactor CP isadditionally provided with contacts CP4-6, contactor C1A with contactsC1A4-5, contactor C2A with contacts C2A4-5 and contactor CSA withlcontacts C3A4-5, also shown in Fig. 3B, for operation as hereinafterdescribed. v

The master control system shown in Figs. '3A-B is connectable at itsupper portion through lines L1-2 for energization from theaforementioned powersupply source. Lines L1-2 of Fig. 3A may beconnected to the lower ends of lines L1-2 of Fig. 2. The masterY controlsystem comprises a master switch MS, preferably of the manually operateddrum type, shown in layout development at the left-hand portion of Figs.3A-B. Switch MS is provided with fifteen contacts MSl-IS, contactsMSI-3, MSS-6 and MS10-1S being normally open and contacts MS4- and MS7-9being normally closed when the switch is in its center Off position.Switch MS is further provided with four Hoist operating positions andfour Lower operating positions, the switch being successively operablethrough the Hoist positions by rotation of the drum in the direction ofthe left-hand arrow shown at the upper portion thereof and beingsuccessively operable through the Lower positions by rotation of thedrum in the opposite direction as indicated by the right-hand arrow. Ineach of the operating positions of master switch MS, the closedcondition of contacts MSI- is indicated by an X in horizontal alignmentwith the respective contacts while absence of an X indicates an opencondition of the respective contacts.

A full-wave rectifier bridge RT2 at the upper portion of Fig. 3A isconnected at its input terminals for energization across lines L1-2through conductors 14 and 16, while another full-wave rectilier bridgeRTS at the lower portion of Fig. 3B is connected at its input terminalsthrough conductors 18 and 20 to lines L1-2, respectively. Although tworectiiier bridges have been shown for ease of illustration, it will beapparent that a single bridge or a separate D.C. source could beemployed in place thereof.

Operating coil HH1 of hold motor hoisting contacter HH is connectedacross lines L1-2 through contacts MSI, conductor 22, normally closedcontacts 24a of Dump switch 24, normally closed contacts SW1 of ahold-ropechange selector v`switch SW and normally closed interlockingcontacts HL6 of hold motor lowering contactor HL. A hold motor brakerelay HBR is provided having an operating coil HBRI connected forenergization through contacts MSl and then in parallel with contactor HHthrough conductor 26, normally open contacts HHS and HLS in parallel,and conductor 16. A close motor brake relay CBR is provided having anoperating coil CBR1 likewise connected for energization through contactsMSI and then in parallel with contacter HH through conductor 26,normally open contacts CHS and CLS in parallel, and conductor 16.

Winding HB1 of hold motor brake HB and winding CB1 of close motor brakeCB are connected through normally open contacts HBRZ and CBR2,respectively, for energization across the positive and negative outputterminals of rectifier bridge RT2.

Operating coil HL1 of the aforementioned contactor HL is connected.across lines ,L1-2"'through normally closedA interlocking contactsHH6,normally open con1 tacts SW2, normally closed contacts 24b of Dumpswitch 24 and contacts MS2. Operating coil CHI of the aforementionedcontactor CH is connected across lines Ll-Z in a circuit extendingthrough normally closed interlocking contacts CLG and normally closedcontacts SW3 where it divides. One branch extends through normallyclosed contacts LLRZ of a load lowering relay LLR and then in a rstcircuit through contacts MSS to line L1, and a second circuit throughnormally open contacts CLR2, 1VR2 and TR2 of relays CLR, IVR and TR,respectively, and contacts MS4 to line L1; while the other branchextends through normally open contacts LLRS and M86 to line L1. Aholding circuit for operating coil HHI is provided from the junction ,ofcontacts CLRZ and LLRZ to the junction of conductor 22 and contacts 24athrough normally open contacts CHG and HH7. Relay CLR has an operatingcoil CLRl connected through contacts MSS across lines L1-2 and normallyopen contacts CLR3 for establishing a holding circuit for its operatingcoil from the junction of the latter and contacts MSS to the junction ofcontacts CLRZ and LLR2. Operating coil CLI of the aforementionedcontactor CL is connected across lines L1-2 through normally closedinterlocking contacts CH7 and normally closed contacts SW4, LLR4, CLR4and MS6. Operating coil TR1 of the aforementioned timing relay TR isconnected across lines L1-2 through contacts MS6 and a half-waverectifier 27. Coil TR1 is shunted by series connected resistor 28 andcapacitor 30 to retard deenergization thereof as hereinafter described.

Hold motor secondary resistance commutating contactors HIL, H2L and HSLhave their respective operating coils H1L1, H2L1 and H3L1 connectedacross lines L1-2 in 4a circuit extending from line L2 through normallyopen contacts HHS where it divides. branch extends through coil H1L1,normally closed contacts LLRS, 2VR2 and CLRS in parallel, DR2 and MS7 toline L1; another branch extends through coil H2L'l and normally closedcontacts LLR6, DR3 Iand M83 to line L1; while a third branch extendsthrough coil H3L and normally closed contacts LLR7, DR4 and M89 to lineL1.

Close motor secondary resistance commutating contactors ClL and C2L havetheir respective operating coils C1L1 and C2L1 connected across linesL1-2 in a circuit extending from line L2 through normally open contactsCHS and CL7 in parallel to a common connection 32 where it divides. Onebranch extends through coil C2L1, normally closed contacts CLR7 andcontacts M510 to line L1 while the other branch extends through coilC1L1, normally closed contacts CLRS and contacts M511 to line L1.Another circuit for coil C2L1 extends from line L1 through contacts MS7and DRZ and normally open contacts CLR6.

The remaining close motor secondary resistance com mutating contactorsCP, C1A, C2A, CSA and C4A have their operating coils connected forenergization across lines L1-2 in a five branch .circuit extending fromline L2 through normally open contacts CH9 where it divides. One branchextends through operating coil CP1 and then by w-ay of parallelconnections through normally open contacts LLRS to line L1 and throughcontacts M812 to line L1. A second branch extends through operating coilC1A1, normally open contacts CP4, normally closed contacts 1A'l`2 of anaccelerating timer relay 1AT, normally open contacts DTZ and DR6 inparallel with normally closed contacts DT3 and DR7 of timer relay DT andDIG relay DR, respectively, and contacts M813 to line L1. A third branchextends through operating coil C2A1, normally open contacts C1A4,normally closed contacts 2AT2 of an accelerating timer relay ZAT andcontacts MS14 to line L1; Av fourth branch extends throughoperating coilC3'A1, normally open contacts C2A4, normally closed contacts 3AT2 'of anaccelera-ting timerrelay'SAT and contacts M815 to'. line L1.

One

And a fifth, branch extends through normally open ccntacts C3A4,operating coil C4A1, normally closed contacts 4ATZ of an acceleratingtimer relay 4AT and contacts MSIS to line L1.

The remaining hold motor secondary resistance commutating contactors HP,HIA, HZA, HSA and H4A have their operating coils connected forenergization across lines LI-Z in a tive branch circuit extending fromline LZ through normally open contacts HH9 where it divides. One branchextends through operating coil HP1, normally closed contacts DR5 andcontacts MSIZ to line L1. A second branch extends through operating coilHIAI and normally open contacts HP4 to the junction of theaforementioned contacts CP4 and IATZ in the energizing circuit of coilCIAI. A third branch extends through operating coil H2A1 and normallyopen contacts H1A4 to the junction of the aforementioned cont-acts CIA4and ZATZ in the energizing circuit of coil CZAI. A fourth branch extendsthrough operating coil HSAI and normally open contacts HZA4 to thejunction of the aforementioned contacts CZA4 and SATZ in the energizingcircuit of coil CSAI. And a fifth branch extends through operating coilH4AI and normally open contacts H3A4 to the junction of theaforementioned coil C4AI and contacts 4ATZ.

Operating coil DRI of DIG relay DR is connected across lines LI-Zthrough a normally open pushbutton foot switch 34. Operating coil LLRIof the aforementioned load lowering relay LLR is connected across linesLI-Z through a normally open pushbutton Lower Load switch 36. A clutchcontrol relay CCR is provided for controlling clutch winding CWI ofclutch CW (Fig. l) and has an operating coil CCRI connected across linesLI-Z through normally closed contacts CPS and HPS and normally opencontacts HHIt).

The aforementioned clutch winding CWI, timer relay DT and acceleratingtimer relays IAT, ZAT, SAT and 4AT are connected in parallel forenergization across the positive and negative output terminals of theaforementioned rectifier bridge RTS. More specically, winding CWI isconnected through conductor 38 and normally open contacts CCR2 acrossbridge RTS. Operating coil DTI is connected through conductor 40 andnormally open contacts DRS; operating coil IATI is connected throughconductor 4Z and normally closed contacts CPG and HP6; operating coilZATI of relay ZAT is connected through conductor 44 and parallelconnected, normally closed contacts CIAS and HIAS; operating coil SAT1`of relay SAT is connected through conductor 46 and parallel connected,normally closed contacts C2A5 and H2A5; and operating coil 4AT1 of relay4AT is connected through conductor 48 and parallel connected, normallyclosed contacts CSAS and HSAS across the output terminals of rectifierbridge RTS.

`Operating coil DTI of timer relay DT is shunted by series connectedresistor 5t) and capacitor 52 to render contacts DTS timed closing, asindicated by T.C. adjacent the latter, when coil DTI is deenergized.Contacts DTZ are instantaneous closing upon energization of operatingcoil DTI as indicated by I.C. adjacent the contacts. Similarly, contactsIATZ, ZATZ, SATZ and 4ATZ of accelerating timer relays IAT, ZAT, SAT and4AT, respectively, are rendered timed closing by series connectedresistor 54 and capacitor 56 shunting operating coil IATI, seriesconnected resistor 58 and capacitor 60 shunting operating coil ZATI,series connected re sistor 62 and capacitor 64 shunting operating coilSAT1, and series connected resistor 66 `and capacitor 68 shuntingoperating coil 4AT1, when the corresponding operating coils aredeenergized.

Let is be assumed that power is supplied to lines L-S of Fig. 2 andthrough lines L I and LZ to the master control system ofrFigs. 3A and3B. Let it also be assumed that master switch MS is in its central Oposition. Rectier bridges RTZ and RTS are energized across lines LI-Zthrough conductors I4, i6 and i8, Ztl, respectively. Timing relays IAT,ZAT, SAT and 4AT are energized in parallel across the positive andnegative output terminals of bridge RTS in a first branch extendingthrough conductor 42, operating coil IATI and contacts CP6 and HPS; in asecond branch extending through conductor 44, operating coil ZATI andthen through contacts CIAS and HIAS in parallel; in a third branchextending through conductor 45, operating coil SAT1 and then throughcontacts CZAS and HZAS in parallel, and in a fourth branch extendingthrough conductor 48, operating coil 4ATI and then through contacts HSASand CSAS in parallel. Capacitors 56, 60, 64 and 68 charge in parallelwith the aforesaid operating coils, respectively. Relays IAT, ZAT, SATand 4AT open respective timed closing contacts IATZ, ZATZ, SATZ and 4ATZin the energizing circuits of the hold and close motor acceleratingcontactors to alford timed acceleration as hereinafter described.

Let it further be assumed that the aforementioned bucket is open and ina raised position and that it is desired to lower the open bucketpreparatory to digging. This is :accomplished by operating master switchMS through Lower operating positions I, 2, S and 4 to accelerate thebucket and back to the Off position to stop the latter.

The graph in Fig. 4, wherein bucket speeds in terms of percent motorsynchronous speed are plotted against torque per motor in terms ofpercent motor torque, depicts in the upper portion thereof bucket speedsattained at speed points l through 4 (corresponding to Hoist operatingpositions 1-4 of master switch MS) when hoisting a loaded bucket withboth the holding and closing lines. The curves in the lower portion ofFig. 4 depict bucket speeds at speed points l through 4 (correspondingto Lower operating positions 1 4 of master switch MS) when lowering anopen bucket with both lines as hereinafter more fully described.Vertical line LBW upstanding at the 100 percent motor torque pointindicates the constant motor load or loaded bucket weight in thehoisting direction in terms of percent motor torque (per motor), whilevertical line OBW depending from the approximately percent motor torquepoint indicates the constant motor load or open bucket weight in thelowering direction in like terms. The horizontal distance between linesLBW and OBW is accounted for by losses such as friction in the gearing.

As hereinafter more fully described in connection with Figs. 2, 3A and3B, when the master control system is set at speed point l for hoisting,the loaded bucket accelerates from zero speed along and as depicted bycurve 11H, Fig. 4 to a stable speed at approximately 20 percent motorsynchronous speed whereat bucket speed curve IH intersects the loadedbucket weight line LBW. At this point the hoisting torque is equal tothe load. Operation of the master control system to speed point 2results in an increase `in hoisting torque effecting furtheracceleration of the bucket as depicted by curve ZH to approximately 52percent speed Whereat bucket speed curve 2H intersects line LBW.Similarly, operation of the master control system to speed points 3 and4 results in acceleration of the bucket as depicted by curves SH and 4H,respectively, to attain a final bucket speed of approximately percentmotor synchronous speed.

When the master control system is set at speed point l for lowering, theopen bucket accelerates along curve IL to a stable speed atapproximately 20 percent motor synchronous speed whcreat curve ILintersects the open bucket weight line OBW. Similarly, operation of themaster control system to speed points 2 land 3 results in accelerationof the bucket as depicted by curves ZL and SL, respectively, to attain aresultant bucket speed of IO() percent motor synchronous speed. Anessential feature of the invention resides in improved apparatus here- 7inafter more fully described effective in speed point 4 for acceleratingthe open bucket up to and above 150 percent motor synchronous speed asdepicted by curve 4L.

Operation of master switch MS to Lower operating position l results inclosure of contacts MSI, 4MS2 and M56 while contacts M84 and MS7-9remain closed. Closure of contacts MSI completes an energizing circuitfor operating coil HlHl of hold rnotor hoisting contactor HH acrosslines Lil-2 through conductor 22 and contacts 24a, 'SW1 and HL. Closureof contacts MS2 of the master switch is without eiect at this time whilecontacts M86 complete energizing circuits across lines L1-2 foroperating coil CL1 of close motor lowering contactor CL through contactsCLR4, LLR4, SW4 and CH7 and for operating coil TR1 of timing relay TRthrough rectifier 27. Contactor HH closes contacts HHZ-d tocomplete'power connections to the primary winding of hold motor HMthereby to energize the latter in the hoisting direction. Contactor -HHalso closes contacts HHS to complete an energizing circuit for operatingcoil HBRI of hold motor brake relay HBR across lines L1-2 throughcontacts MSI and conductors Z6 and 16. Relay HBR closes contacts HBRZ tocomplete an energizing circuit for hold motor brake winding HB1 acrossthe positive and negative output terminals of rectiiier bridge RT2. As aresult brake HB is disengaged to permit operation of the hold motor ashereinafter described. Contactor HH opens interlocking contacts -Hl-l toprevent concurrent energization of hold motor lowering contactor HL andcloses contacts HH7-10. Contacts HH? prepare a holding circuit forcontactor HH While contacts HHS complete three parallel circuits acrosslines L1-2 for energizing operating coil H1L1 in a first branchextending through contacts LLRS, contacts ZVRZ and CLRS in parallel andcontacts DRZ and MS7, for energizing operating coil H2L1 in a secondbranch extending through contacts LLR6, DR3 and MSS and for energizingoperating coil H3L1 in a third branch extending through contacts LLR7,DR4 and M39. Contactors HSL, H2L and HIL close their respective pairs ofcontacts H3L2-3, H2L2-3 and HILZ-S to shunt resistor groups R1-3effectively out of the secondary resistance network of hold motor HM. Asa result hold motor HM develops a predetermined value of torque in thehoisting direction as hereinafter more fully described in connectionwith Fig. 5. Contacts HH9 perform no useful function at this time whilecontacts HH10 complete an energizing circuit for operating coil CCR1 ofclutch control relay CCR across lines L1-2 through contacts CPS and HP5.Relay CCR energizes and closes contacts CCR2 to complete an energizingcircuit for winding CWI of clutch CW (Fig. 1) across the positive andnegative output terminals of rectifier bridge RTS through conductor 38.As a result clutch CW engages to couple the hold and close motorsthrough shafts 2 and 4 t'or operation in unison.

The aforementioned energization of close motor lowering contactor CLresults in closure of` contacts CL2-4 (Fig. 2) to complete powerconnections to the primary winding of close motor CM thereby to energizethe latter in the lowering direction. Contactor CL also closes contactsCLS to complete an energizing circuit for operating coil CBRl of closemotor brake relay CBR in parallel with series connected coil HBRl andcontacts HHS. Relay CBR closes contacts CBRZ to complete an energizingcircuit for close motor brake winding CB1 across rectifier bridge RT2.Energization of winding CB1 disengages close motor brake CB (Fig. l) topermit operation of the close motor in the lowering direction. ContactorCL opens interlocking contacts CL6 to prevent concurrent energization ofthe close motor hoisting contactor CH, and closes contacts CL7 toprepare parallel energizing circuits for operating coils CZLI and C1L1of close motor secondary resistance commutating contactors CZL and CIL,respectively, to be successively completed upon movement of masterswitch MS to the second and third lowering positions as hereinafterdescribed. The aforementioned energization of timing relay TR results inclosure of contacts TR2 which close a point in the energizing circuitof-contactor CH.

The graph shown in Fig. 5, wherein speeds in terms of percent motorsynchronous speed are plotted against percent motor torque (per motor),depicts the operating characteristics of the holding and closing linesand the bucket. Curves 1H, 2H, 3H, and 4H in the upper righthand portionof Fig. 5 and curves 1L, 2L, 3L and 4L in the lower right-hand portionthereof, representing the effects of -the holding and closing lines onthe bucket, are similar to the corresponding curves in Fig. 4hereinbefore described while vertical lines LBW and OBW depict theloaded and open bucket weights, respectively, as aforesaid. Curve 3HA inthe upper right-hand portion of Fig. 5 depicts an additionalacceleration step provided in Hoist speed point 4 by retardedenergization of commutating contactors C4A and H4A through slow-actingcontacts of timing relay 4AT as hereinafter described.

- Curves HlL, H2L, HSL and H4L in the lower righthand portion of Fig. 5depict the speed torque characteristics of the holding lines in the rst,second, third and fourth lowering positions, respectively, of the mastercontrol system. Curves ClL, CZL and CSL in the lower left-hand portionand curve C4L in the lower right-hand portion of Fig. 5 depict the speedtorque characteristics of the closing lines in the first, second, thirdand fourth lowering positions, respectively, of the master controlsystem. It will be observed as the description proceeds that the lowerright-hand quadrant represents lowering motion concurrently withhoisting energization or torque while the lower left-hand quadrantrepresents lowering motion concurrently with lowering energization ortorque.

As a result of the aforementioned energization of the hold motor in thehoisting direction as depicted by curve HIL in Fig. 5 and energizationof the close motorin the lowering direction as depicted by curve CIL,the bucket Starts lowering along curve 1L. The weight of the open bucketis sufficient to fully load the hold motor when the latter is energizedfor hoisting as shown by the intersection of bucket weight line OBW withthe horizontal zero speed line at percent torque and the intersection ofcurve HIL with the latter at approximately 70 percent torque, thus toafford the close motor control over movement of the bucket. Close motorCM accelerates in the lowering direction and, being coupled to holdmotor HM through clutch CW as aforesaid, drives the hold motor in thelowering direction, increasing the counter-torque provided by the holdmotor as shown by curve HIL until counter, hoisting torque portion Xcounterbala'nces the lowering torque X at approximately 2O percentlowering speed.

When hold motor HM reaches l0 percent of its synchronous speed, thevoltage induced in its secondary Winding is suiiicient to energizeoperating coil 1VR-1 of voltage relay 1VR, Fig. 2. Relay 1VR closescontacts IVRZ, Fig. 3A, to close another point in the aforementionedenergizing circuit of contactor CH.

In order to further accelerate lowering of the bucket, master switch MSis moved to Lower operating position 2 to open contacts MS7 and closecontacts M510. ContactsMS7 interrupt the energizing circuit of operatingcoil H1L1- to release contactor HIL and open contacts H1L7f-3 in thehold motor secondary resistance network. As a result, resistor group R3is reinserted eltectively in the network to decrease the hold motorcounter, hoisting torque as shown by curve H2L in Fig. 5, thus toenhance acceleration of the bucket in the lowering direction.

vContacts M810 complete the energizing circuit of operating coil C2L1 ofcontactor C2L through contacts CLR7 and CL7. Contactor CZL closescontacts C2L23, Fig. 2, to shunt resistor group R11 effectively out ofthe close motor secondary resistance network. As a result, close assensomotor CM develops an increased lowering torque as shown by curve C2L toaccelerate the bucket along curve 2L, drives hold motor HM in thelowering direction ncreasing the countertorque as shown by curve H2Luntil countertorque portion Y counterbalances the lowering torque Y atapproximately 55 percent speed whereat the bucket speed line 2Lintersects the open bucket weight line OBW.

Moving master switch MS to Lower operating position 3 results in openingof contacts MSS and closure of contacts MS11. Contacts MSS interrupt theenergizing circuit of operating coil H2L1 to release Contactor H2L andopen contacts H2L2-3 in the hold motor secondary resistance network. Asa result, resistor group R2 is reinserted effectively in circuit todecrease the hold Inotor counter, hoisting torque another step as shownby curve H3L in Fig. 5 and permit further acceleration of the bucket.Contacts MS11 complete an energizing circuit for operating coil C1L1 ofcontactor C1L through contacts CLR8 and CL7 whereupon contacts C1L23close to shunt resistor group R12 effectively out of the close motorsecondary resistance network. As a result, close motor CM furtherincreases the lowering torque as shown by curve C3L in Fig. 5 toaccelerate the bucket along curve 3L, driving the hold motor reverselyand increasing the countertorque as shown by curve HSL until a balancedcondition is reached at 100 percent speed as shown by the intersectionof curves 3L and H3L with line OBW in Fig. 5.

When hold motor HM is driven to 80 percent of its synchronous speed, thevoltage induced in its secondary winding becomes sutiicient to energizeoperating coil 2VR1 of voltage relay 2VR, Fig. 2, whereupon the latteropens contacts 2VR2, Fig. 3A, to prevent reenergization of contaotor H1Lduring subsequent speed checking until the bucket speed has decreased to80 percent as hereinafter described.

Moving master switch MS to Lower operating position 4 results in closureof contacts MSS and opening of contacts MS9-11. Contacts MSS complete anenergizing circuit across lines L1-2 for operating coil CLRI of relayCLR while contacts MS9-11 interrupt the energizing circuits of operatingcoils H3L1, C2L1 and C1L1, respectively, to release contactors H3L, C2Land C1L. Contacts H3L2-3 open to reinsert resistor group R1 eectively inthe hold motor secondary resistance network to decrease the hold motorcounter, hoisting torque another step as shown by curve H4L in Fig. 5and permit further acceleration of the bucket. Contacts C2L2-3 and C1L23open to reinsert resistor groups R11 and R12 effectively in the closemotor secondary resistance network for reasons hereinafter described.

Relay CLR being energized as aforesaid opens contacts CLR8 and CLR7 toprevent reenergization of commutating contactors C1L and C2L as themaster switch is subsequently moved back through operating position 3 toposition 2. Contacts CLR6 close to prepare an energizing circuit foroperating coil C2L1 to be subsequently completed upon movement of masterswitch MS back to Lower operating position l. Contacts CLRS open toplace `Contactor HIL under the control of voltage relay ZVR and preventreenergization of comniutating contactor HIL until the bucket speeddecreases to 8O percent should the master switch be rapidly moved to itsOif position. Contacts CLR4 open to interrupt the energizing circuit ofoperating coil CL1 While contacts CLRZ close to complete the energizingcircuit of operating coil CHL through contacts M84, TR2, 1VR2, CLR2,LLR2, SW3 and CL6, the latter contacts CL6 closing in response todeenergization of operating coil CL1. As a result, contactor CL openscontacts CL2-4 and Contactor CH closes contacts CH2-4 to reverse theenergization of close motor CM from the lowering to the hoistingdirection as shown by curve C4L in the lower right-hand quadrant of Fig.5. Relay CLR also closes contacts CLR3 to complete a holding circuit forits operating coil through contacts M55-"i, TR2, lVRZ and CLRZ. Theclosure of contacts CHS and CHS of contactor CH maintains the circuitsinterrupted by contacts CLS and CL7 of Contactor CL. Contacts CH6 closeto complete the aforementioned holding circuit for contacter HH,interlocking contacts CH? open to prevent reenergization of contactorCL, and contacts CH9 close without effect at this time.

Although both the hold motor and close motor are now energized in thehoisting direction, the bucket accelerates in `the lowering directionalong curve 4L in Fig. 5. The resistance of group R1 which wasreinserted in the hold motor secondary network in going from Lower speedpoint 3 to speed point 4 is of relatively large value, approximatelyequal to the combined resistances of groups R2 and R3. Thus, reinsertionof resistor group Rit decreases the hold motor counter, hoisting torquea substantial amount Z as shown in Fig. 5 Whereas the reversal ofenergization of the close motor to the hoisting direction with all ofits secondary resistance in circuit develops a relatively smaller valueof torque Z opposing lowering of the bucket. The resultant countertorqueZ" opposing lowering of the bucket is less than the bucket Weight OBW atpercent speed as shown in Fig. 5 so that the bucket accelerates alongcurve 4L up to approximately to 175 percent motor synchronous speed inactual practice.

As the bucket approaches its lowermost position it is desired to checkthe speed thereof. This is attained by moving the master switch from thefourth to the third Lower operating position or, in order to stop thebucket, all the Way to the lirst Lower operating position or to Offposition.

Movement of master switch MS to the third Lower operating positionresults in opening of contacts MSS without effect as relay CLR ismaintained energized through contacts CLRZ and CLR3, and closure ofcontacts MS9-11. Contacts MS10 and MSH close without effect as contactsCLR7 and CLR8 are open while contacts M89 complete the energizingcircuit of operating coil H3L1 of Contactor HSL through contacts DR4,LLR7 and HHS.

The graph in Fig. 6, wherein bucket speeds in terms of percent motorsynchronous speed are plotted against percent motor torque (per motor),depicts in the lower right-hand quadrant thereof the bucket speedchecking characteristics of the invention. Vertical line OBW depicts theopen bucket weight as described in connection with Figs. 4 and 5. CurveC4L depicts the speed torque characteristics of the close motor forLower operating position 4 and corresponds to the like curve in Fig. 5.The speed torque characteristics of the close motor remain unchanged atcurve C4L as the lowering speed is checked by moving master switch MS toLower operating position 3 and therethrough to position 2. This isattained by virtue of commutating contactors CZL and C1L beingmaintained deenergized at the then open contacts CLR7 and CLRS,respectively. Curve H4L depicts the speed torque characteristics of thehold motor for Lower operating position 4 and corresponds to the likecurve in Fig. 5. Curve HSL depicts the speed torque characteristics ofthe hold motor for Lower operating position 3, curve H2L for position 2and curve HIL for operating position l and correspond to like curves inFig. 5. Curve HdL being coincident with curve C1L in addition depictsthe speed torque characteristics of the close motor for Lower operatingposition l as hereinafter more fully described.

Contactor HSL being energized as a result of checking bucket speed tospeed point 3 as aforementioned closes contacts H3L2-3 to shunt resistorgroup R1 effectively out of the hold motor secondary resistance network.This shifts the speed torque characteristics of the hold motor fromcurve H4L to H3L which in combination with close motor curve C4L aords aresultant hoisting gazeuse torque such that the bucket decelerates alongcurve SG1, Fig. 6.

Y Moving master switch MS to Lower operating position 2 effects closureof contacts MSS to complete the energizing circuit of operating coilHZLl of contactor H2L through contacts DRS, LLR6 and HHS. As a result,resistor group R2 is shunted eiectively out of circuit. This shifts thespeed torque characteristics of the hold motor from curve H3L to H2Lwhich in combination with close motor curve C4L affords a resultantcountertorque such that the bucket decelerates along curve SC2, Fig. 6.

Moving master switch MS to Lower operating position l eects closure ofcontacts MS7 to complete an energizing circuit for operating coil CZLlof contactor C2L through contacts DR2, CLR6 and CHS. Contactor C2Lcloses contacts C2L2-3 to shunt resistor group R11 eectively out ofcircuit. This shifts the close motor speed torque characteristic fromcurve C4L to curve CIL coinciding with curve HftL to enhancedeceleration of the bucket. Assuming that the speed has decreased to avalue below 80 percent resulting in deenergization of voltage relay ENRin Fig. 2 and closure ot' contacts ZVRZ in Fig. 3A, contacts M57 alsocomplete an energizing circuit for operating coil I-IlLl of contactorHlL through contacts DRZ, 2VR2, LLRS and HHS. Contactor HEL closescontacts HlLZ-Ei to shunt resistor group R3 effectively out of circuit.This shifts the speed torque characteristic of the hold motor from curveH2L to HIL to further decelerate the bucket.

Moving master switch MS to the Oft position results in opening ofcontacts MSI, MS2 and MS6. Contacts MST interrupt the originalenergizing circuit of contactor HH but the latter is maintainedenergized through the aforementioned holding circuit to prevent brakingthe motors until their speed decreases to a safe value. Contacts MS2open without effect while contacts M86 interrupt energization of timingrelay TR. Capacitor 3i) begins to discharge through resistor 28 andoperating coil TR1 to retard opening of contacts TR2.

When the speed decreases to 10 percent, voltage relay llVR openscontacts lVRZ to deenergize relay CLR, hoisting contactors CH and HH andbrake relays CBR and HBR. Relay CLR opens contacts CLR6 to interruptenergization of contactor CZL to reinsert resistor group R11 eiiectivelyin circuit. Contactors CH and HH disconnect power from the motors whilecontactor HH also opens contacts HHS to interrupt energization ofcontactors HELL, H2L and HSL to reinsert resistor groups Ril-3eiiectively in circuit. Relays CBR and HBR open contacts CBRZ and- HBR2,respectively, to interrupt energization of brake windings CB1 and HB1 toset the close and hold motor brakes.

g The timing of relay TR is set so that contacts TR2 open approximatelyone second after opening of contacts tVRZ. This is a sacty measure toinsure that the motors stop in the event contacts 1VR2 fail to open.

it should be observed that in the event master switch MS is rapidlymoved from Lower operating position 4 to operating position l or to Offposition, sudden deceleration of the bucket is automatically prevented.This is accomplished by voltage relay ZVR maintaining contacts ZVRZ opento delay energization of contactor HIL until the speed decreases to 80percent. As graphically shown in Fig. 6, the hold motor speed torquecharacteristic follows curve H2L until the speed decreases to S0 percentand then shifts to curve HllL. Thus, the bucket always decelerates alongcurve SCl when checking the speed from the fourth to the third Lowerspeed point and decelerates along curve SC2 when checking the speed tothe second or iirst speed point or to OH position to affordsmoothdeceleration. AtA 80 percent speed, the aforesaid characteristicshifts from curve H2L to HIL to further decelerate the bucket.

j, ln .the event master switch MS is rapidly movedfrorn Lower operatingposition 4 to the Oi position and relay ZVR fails to function, suddenbraking of the motors is automatically prevented by timing relay TR.When the energizing circuit of timing relay TR is interrupted in the Oiposition as aforementioned, capacitor 30 begins to discharge throughresistor 28 and operating coil TR1 to retard opening of contacts TR2 fora predetermined time interval to permit the bucket to slow down to asafe value. At the end of such time interval contacts TR2 open toinitiate braking of the motors as hereinbefore described in connectionwith release of voltage relay 1VR.

To perform a digging operation in order to fill the bucket with ore orother material being unloaded, DlG switch 34 is pressed andsimultaneouslymaster switch MS is moved through Hoist operatingpositions 1, 2 and 3 to position 4.

Pressing DIG switch 34 completes an energizing circuit for operatingcoil DRI of DIG relay DR across lines L1-2. Relay DR opens contacts DR25to prevent energization of contactors HIL, H2L, H3L and HP, closescontacts DR6 to prepare an energizing circuit for contactor C1A, openscontacts DR7 for reasons hereinafter described, and closes contacts DRSto complete an energizing circuit for operating coil DTI of timing relayDT through conductor 40. Relay DT closes contacts DTZ to close anotherpoint in the energization circuit of contactor C1A and opens contactsDTS to place contactors C1A. CZA. C3A and C4A under control of DIGswitch 34 as hereinafter described.

Movement of master switch MS to Hoist operation position l results inclosure of contacts MSl, MSS and MSltl- 12 while contacts M574) remainclosed and opening of contacts MS-fi. Contacts MSI complete the abovetraced energizing circuit for contactor HH which closes contacts HHZ-tto energize hold motor HM in the hoisting direction. Contacts MSScomplete an energizing circuit for operating coil CHI of contactor CHthrough contacts LLRZ, SW3 and CL6. Contacts MSN-12 close points in theenergizing circuits of operating coils C2L1, C1L1 and CP1. Contactor HHalso closes contacts HHS to energize relay HBR which in turn at contactsHBR2 energizes winding HB1 of hold motor brake HB to disengage thelatter, closes contacts HH7 to prepare a shunt circuit across contactsMSI, closes contacts HHB without effect as contacts DR2-4 are open, andcloses contacts HH9 to prepare energizing circuits for operating coilsHP1, HlAl, HZAl, HSAE and H4A1. Contactor CH closes contacts CH2-4 toVenergize close motor CM in the hoisting direction, closes contacts CHSto energize relay CBR which in turn at contacts CBRZ energizes windingCB1 of close motor brake CB to disengage the latter, closes contacts CHSto complete the aforementioned shunt circuit across contacts MSl throughcontacts HH7 and MSB: to maintain energizationfof contactor HH, closescontacts CHS to complete energizing circuits for operating coil C2L1through contacts CLR7 and M510 and for operating coil ClLl throughcontacts CLRS and M811, and closescontracts CH9 to complete theenergizing circuit of operating coil CP1 through contacts MSM.Contactors CZL, CIL and CP close respective contact pairs C2L2-3, C1L2-3and CP2-3 to shunt resistor groups R11-13 effectively out of circuit.Contactor CP also closes contacts CP4 to close a point in the energizingcircuit of operating coil ClAl, opens contacts CPS to preventenergization of relay CCR, and opens contacts CP6 to interrupt theenergizing circuit of timing relay IAT. Capacitor 56 begins to dischargethrough resistor 54 and operating coil lATl, and after a time intervalcontacts 1AT2 close another point in the energizing circuit of contactorC1A.

Moving master switch MS to Hoist operating positions 2, 3 and 4 resultsin successive closure of contacts M813, M514 and MSlS. In Hoistoperating position 2 contacts M81, MSS and MS7-12 remain closed andcontacts MSl complete the energizing circuit of contactor C1A.throughcontacts DR, DTZ, IATZ, Clfi, yoperating coil C1A1 and contacts CH9.Contacter C1A closes contacts C1A2-3 to shunt resistor group R14eiectively out of the close motor secondary resistance network.Contactor C1A also closes contacts C1A4 to prepare an energizing circuitfor operating coil C2A1 or" contactor CZA and opens contacts C1A5without eiect at this time.

In Hoist operating position 3 contacts MSI, MSS and MS7-13 remain closedand contacts MSI/i close while in Hoist operating position 4 contactsMS1, MSS and MS'7-14 remain closed and contacts M515 close without eiectas timing relays 2AT, SAT and 4AT maintain the energizing circuits ofcontactors CZA, C3A and C4A open at contacts 2AT2, SATZ and 4AT2,respectively.

As a result of the aforementioned operations, resistor groups R-18remain effective in the close motor secondary resistance network whileresistor groups R1-9 remain eiective in the hold motor secondaryresistance network. Consequently, the close motor develops a greatertorque than the hold motor and the bucket begins to close. As the bucketdips into the pile, it pulls down against a light, stalled, hold motortorque (equal to that developed by the hold motor in Lower speed point4) to keep the holding lines taut while permitting the bucket to settle.

Should the close motor approach a stalled condition when digging, theDIG switch may be momentarily released to eiTect hoisting the bucket adesired amount thereby facilitating power closing of the bucket. Releaseof DIG switch 34 interrupts energization of DIG relay DR which closescontacts DRZ-S to complete the energizing circuits of operating coilsHlLl, HZLI, H3L1 and HP1. Relay DR also opens contacts DR6 to interruptenergization of contacter C1A, closes contacts DR7 to prepare a parallelenergizing circuit for contacter C1A, and opens contacts DRS tointerrupt energization of timing relay DT. Relay DT opens contacts DTZto further interrupt the circuit of contacter C1A. Capacitor 52 beginsto discharge through resistor 50 and operating coil DT1 and after a timeinterval contacts DTS close the aforesaid parallel energizing circuitfor contacter C1A. This time interval is sufficiently long to permitdeenergization of contactor C1A preparatory to timed acceleration ofboth the hold and close motors in the hoisting direction. Theaforementioned energization of contactors HSL, H2L, HIL and HP resultsin closure of contacts H3L2-3, H2L2-3, H1L2-3 and HP2-3 to shuntresistor groups Rl-i etrectively out of circuit. Contactor HP alsocloses contacts HP4 to prepare the energizing circuit for contacter H1A,opens contacts HPS to further interrupt the energizing circuit of clutchcontrol relay CCR, and opens contacts HPS to open `.another point in thetiming relay IAT energizing circuit. When contacts DT3 reclose at theend of the aforesaid time interval, contactors C1A and HIA energize andclose respective contact pairs C1A2-3 and H1A2-3 to shunt resistorgroups R14 and R5 effectively out of circuit. Contacts C1A4 and H1A4close to prepare energizing circuits for contactors CZA and HZA whilecontacts C1A5 and H1A5 open to interrupt energization oi timing relayZAT. Capacitor 6i) begins to discharge through resistor 58 and operatingcoil 2AT1 `and after a predetermined time interval contacts ZATZ closethe energizing circuits or contactors CZA and HZA which close respectivepairs or" contacts C2A2-3 and HZAZ-S to shunt resistor groups R15 and R6effectively out of circuit. Contacts CZA@ and H2A4 close to pre;L areenergizing circuits for contactors C3A and H3A while contacts C2A5 andHZAS interrupt energization of timing relay SAT. Capacitor 601 begins todischarge through resistor 62 and operating coil SAT1 and 'after a timeinterval contacts SATZ close the energizing circuits of contactors CEAand H3A which close respective pairs of contacts C3A2-3 and H3A2-3 toshunt resistor groups R16 and R7 eiiectively out of circuit. ContactsC3A4 and H3A4 close to prepare energizing circuits for contactors CdAand Hit-A while contacts CSAS and HSAS interrupt energization of timingrelay AT. Capacitor 68 begins to discharge through resistor titioperating coil AT1 and after a time interval contacts 4AT2 close theenergizing circuits of contactors C4A and H4A which close respectivepairs of contacts DAZ-3 and H4A2-3 to shunt resistor groups R17 and R5ette-ctively out of the secondary resistance networks.

In actual practice motor secondary resistance commutation rnay notprogress to the extent hereinbefore described as the DIG switch isrepressed as soon as the close motor re-accelerates after stallingwhereupon the bucket continues digging. r/hen the bucket approaches aclosed condition, the DIG switch is released to initiate hoisting of thebucket as hereinbefore described.

if desired, the bucket may be hoisted starting with the master switch inits Off position. Under these conditions, to hoist the loaded bucket,master switch MS is operated through Hoist operating positions l, 2 and3 to position 4. Movement of the master switch to position 1 results inenergization of hold motor hoisting contacter HH, close motor hoistingcontactor CH, hold motor brake relay HBR, close motor brake relay CBR,brake windings HBR and CBR to disengage the motor brakes, hold motorsecondary resistance cornrnutating contactors H3L, H2L, HIL and HP, andclose motor secondary resistance commutating contactors CZL, ClL and CP,all as hereinbet'ore described, whereby the control system is set atHoist speed point l. As a result, the loaded bucket accelerates in thehoisting direction along curve 1H shown in the upper right-hand portionof Fig. 5 up to approximately 20 percent motor synchronous speed whereatcurve 1H intersects the loaded bucket weight line LBW.

Moving master switch MS to Hoist operating position 2 results inenergization of secondary resistance cornmutating contactera HIA and C1Aand deenergization of timing relay ZAT as hereinbefore described toaccelerate the bucket along curve 2H up to approximately 52 percentrated speed whereat curve 2H intersects line LBW. In Hoist operatingposition 3 contactors HZA and CZA energize and interrupt energization ortiming relay 3AT to accelerate the bucket along curve 3H up toapproximately 72 percent speed as shown in Fig. 5. in Hoist operatingposition 4 contactors H3A and CSA energize and interrupt energization oftiming relay 4AT to accelerate the bucket along curve SHA shown in Fig.5 up to approximately 83 percent speed. A predetermined time intervalafter the energizing circuit of relay 4AT is interrupted, contacts 4AT2close and energize contactors H4A and C4A to further accelerate thebucket along curve 4H up to approximately percent motor synchronousspeed.

When the loaded bucket has been hoisted to the desired height, it may bestopped by returning master switch MS to the Oil position. As a resultthe hold and close motors are deenergized and brakes HB and CB are setto hold the bucket. The control contactors and relays are also returnedto their initial conditions in preparation for either lowering theloaded bucket or dumping the load. The apparatus for conveying theloaded bucket to the dumping area is omitted herein for the sake ofsimplicity.

To lower the loaded bucket, Lower Load switch 36 is pressed and masterswitch MS is set at Lower operating position l. Pressing switch 36results in energization oi operating coil LLRl of Lower Load relay LLRwhich closes contacts LLRS to prepare an energizing circuit forcontacter CH and opens contacts LLRZ to prevent establishment of othermaintaining circuits for contacter CH. Relay LLR also opens contactsLLRfi--7 to prevent energization of contactors CL, HIL, H2L and HSL andcloses contacts LLRS to prepare an energizing circuit for contacter CP.

Movement of master switch MS to Lower operating position 1 closescontacts MSl to eitect energization of contactor HH to energize the holdmotor in the hoisting direction, brake relay HBR and winding HB1 todisengage hold motor brake HB. Closure of contacts MS6 energizes timingrelay TR without effect at this time and completes an energizing circuitfor operating coil CH1 through contacts LLR3, SW3 and CL6. Contactor CHcloses contacts CH2-4 to energize the close motor in the hoistingdirection, and closes contacts CHS to energize relay CBR which in turncloses contacts CBRZ to complete an energizing circuit for winding CB1to disengage the close motor brake CB. Contactor CH also closes contactsCH6 and opens contacts CHS, without effect at this time, opens contactsCH7 to prevent concurrent energization of contactor CL, and closescontacts CH9 to complete the energizing circuit of operating coil CP1through contacts LLRS. Contactor CP closes contacts CP2-3 to shutresistor groups R11-13 effectively out of the close motor secondaryresistance network. Contactor CP also closes contacts CP4 without effectat this time, opens contacts CPS to prevent energization of clutchcontrol relay CCR, and opens contacts CP6 to deenergize timing relayIAT, closing contacts 1AT2 which perform no useful function at thistime.

As a result of the aforementioned functions, both the hold motor and theclose motor are energized in the hoisting direction, the hold motorhaving all of its secondlary res-istance effectively in circuit whileresistor groups R11-13 are shunted effectively out of the close motorsecondary resistance network. Consequently, the hold motor develops ahoisting torque, of approximately 20 percent (equal to that developed bythe hold motor in Lower speed point 4 as shown by the intersection ofcurve R4L and the horizontal zero-speed line in Fig. 5) while the closemotor develops a hoisting torque of approximately l25 percent (equal tothat developed by the close motor in Hoist speed point 1 as shown by theintersection of curve 1H and the horizontal zero-speed line in Fig. 5).Let it be assumed that' the material weighs the same amount as the openbucket. Then, deducting the aforementioned friction losses, the combinedweight of the bucket and material is 150 percent. As the totalcountertorque amounts to only about 145 percent, the resultant torgue ofapproximately percent effects lowering of the loaded bucket at a slowspeed. The relatively high countertorque of the close motor maintainsthe bucket closed during lowering. v

When the loaded bucket has been lowered to a desired position, LowerLoad switch 36 is released and Dump switch 24 is pressedto dump theload. Release of switch 36 results in. deenergization of relay LLR whichcloses contacts LLR2 without effect at vthis time, opens contacts LLR3to deenergize contactor CH, and closes contacts LLR4 to complete anenergizing circuit for operating coil CL1 of contactor CL throughcontacts MS6, CLR4, SW4 and CH?, the latter contacts closing uponrelease of contactor CH. As a result the close motor energization isreversed from the hoisting to the lowering direction.

Pressing Dump switch 24 results in opening of contacts 24a to interruptenergization of contactor HH and opening of contacts 24h to preventenergization of contactor HL. Contactor HH opens contacts HH24 todeenergize the hold motor, opens contacts HHS to deenergize brake relayHBR, and opens contacts HH to prevent energization of clutch controlrelay CCR. Relay HBR opens contacts HBRZ to deenergize winding HB1 toset the hold motor brake.

As a result of the aforementioned functions, the hold motor is brakedwhile the close motor operates in the lowering direction to throw thebucket open.

Selector switch SW is employed to slacken the holding lines to permitremoval of a worn hold rope and substitution of another rope in placethereof.v This is preferably accomplished when the open bucket has beenlowered and is resting on the pile. Operation of selector switch SWresults in opening of contacts SW1, SW3 and SW4 and closure of contactsSW2. Contacts SW1, SW3 Vand SW4 open points in the energizing circuitsof 16 power contactors HH, CH and CL, respectively, while contacts SW2prepare an energizing circuit for power contactor HL. Moving masterswitch MS to Lower operating position 1 results in closure of contactsMSL-2.

lContacts MS2 complete an energizing circuit for operating coil HL1 of,hold motor lowering contactor HL through contacts 24b, SW2 and HH6.Contactor HL closes contacts HL2-4 to energize hold motor HM in thelowering direction, closes contacts HLS to complete an energizingcircuit for operating coil HBRl through contacts MS]` and conductors 26and 16, and opens interlocking contacts HL6 to prevent concurrentenergization of contactor HH. Relay HBR closes contacts HBRZ to completean energizing circuit for winding HB1 across rectifier bridge RTZ todisengage hold motor brake HB, Fig. l. Hold motor HM now operates in thelowering direction to slacken the holding lines whereafter master switchMS is returned to its. Oil position to. stop the motor and set-brake HB.

Dump switch 24 may also be employed to close the empty bucket in itsraised position. Pressing Dump switch 24 results in opening of contacts24a and 2411 to prevent energization of power contactors HH or HL.Moving master switch MS to Hoist operating position 1 results in closureof contacts MSS to complete an energizing circuit for operating coil CHlof close motor hoisting contactor CH through contacts LLRZ, SW3 and CL6.Contacts MSN-12 also close to prepare energizing circuits for contactorsCZL, C1L and CP. Contactor CH closes contacts CH2-4 to energize theclose motor in the hoisting direction, closes contacts CH5 to energizerelay CBR which in turn at its contacts CBR2 energizes winding CB1 todisengage the close motor brake, closes contacts CHS to energizecontactors C2L and C1L and closes contacts CH9 to energize contactor CP.Contactors C2L, C1L and CP close their contacts to shunt resistor groupsR11-13 effectively out of the close motor secondary resistance network.As a result, the hold motor is braked and the close motor operates toclose the bucket. Return of master switch MS to Off position stops theclose motor.

From the foregoing, it should be apparent that thev improved buckethoist control not only provides for al1 the required operations but alsoaccomplishes the same in response to manipulation of a single mastercontrol so that the resulting motion attained at the bucket is alwayskept logically in accordance with the direction of movement of themaster control. Thus, no complicated or confusing manual operations arerequired of the operator.

1 claim:

1. ln a system for operating a two-motor bucket hoist having a holdingline motor, a closing line motor, and a selectively engageable clutchmeans for coupling the motors to one another for matched speedoperation, the improvement comprising control means for operating thebucket hoist with a minimum of manual operations, said control meanscomprising a master switch having an off position and a plurality ofhoisting and lowering operating positions, means responsive to settingsaid master switch to a selected lowering operating position foroperating the clutch means to couple the motors for matched speedoperation, means also responsive to said setting of said master switchfor energizing the motors to afford torques in diverse directions, andmeans also responsive to setting of said master switch for automaticallycontrolling the torques of the motors to predetermined values, thetorques developed by the motors and the weight of the bucket effectingcontrolled acceleration of the latter in the lowering direction.

2. The invention defined in claim 1 together with means responsive tosetting of said master switch to another lowering operating position forreversing the energization of one of said motors and concurrentlyaltering the value of torque developed by the other of said motors toaffordvacceleration of the :bucket above'motot. synchronous speed. v

3. The invention defined in claim 2 together with means responsive toresetting said master switch from said other lowering operating positionto the first .mentioned lowering operating position for effecting afirst step of bucket deceleration, and means responsive to motor speedand effective when such speed decreases to a predetermined value forautomatically effecting another step of bucket deceleration thereby toprovide gradual deceleration of the bucket.

4. The invention defined in claim 3 wherein the motors are provided withelectro-responsive brakes, together with means responsive to motor speedand effective when the latter decreases to another predetermined valuefor deenergizing said motors and setting `said brakes, and timing meansresponsive to resetting of said master switch in its off position fordeenergizing s'aid motors and setting said brakes in the event the lastmentioned means fails to operate.

5. In a system for controlling a plurality of motors to lower a load, amaster control switch having a plurality of lowering operatingpositions, means for coupling the motors for operation in unison, meansresponsive to setting of said control switch at a first operatingposition for energizing one of said motors for hoisting and another ofsaid motors for lowering and for engageing said coupling means, thecountertorque developed by said one motor being insufficient to hoistthe load to permit said other motor to accelerate the load in thelowering direction, means responsive to setting of said control switchat a second operating position for decreasing said countertorque andincreasing the lowering torque to further accelerate the load to motorsynchronous speed while maintaining said coupling means engaged wherebysaid other motor drives said one motor reversely to afford matched speedoperation of the motors, and means responsive to setting of said controlswitch at a third operating position for reversing energization of saidother motor to develop a small amount of countertorque and fordecreasing the first mentioned countertorque a greater amount to furtheraccelerate the load above motor synchronous speed.

6. The invention defined in claim 5 together with means responsive toresetting said control switch at said second operating position forincreasing the total countertorque to afford deceleration of the load,and means responsive to setting of said control switch to said firstoperating position for delaying further increase in said totalcountertorque until the load speed has decreased to a predeterminedvalue to afford smooth deceleration t of the load.

7. The combination according to claim 6 together with electro-responsivebrakes for the motors effective to engage in response to deenergizationof the latter, speed responsive means preventing application of saidbrakes until the load speed decreases to a predetermined safe value, andmeans responsive to further resetting of said master switch foreffecting time delay engagement of said brakes to insure stopping ofsaid motors if said speed responsive means fails to operate.

8. In an electrical system for controlling the holding and closing linemotors of a two-motor bucket hoist having a clutch operable to engagethe motors for operation in unison, in combination, a master controlsystem comprising a single drum controller and a control system operableby said drum controller for controlling both the holding and closingline motors and the clutch, said drum controller having a normalposition and a plurality of hoisting operating positions for varying thehoisting speed of the bucket and a plurality of lowering operatingpositions for varying the lowering speed of the bucket, said controlsystem comprising means responsive to setting of said drum controller inselected hoisting operating positions for energizing and adjustablycontrolling the speeds of both of the motors to hoist the bucket, 4meansresponsive to setting of said drum controller in selected loweringoperating positions for energizing the holding line motor for hoistingtorque to support the bucket and for energizing the closing line motorfor lowering-torque and for adjustably controlling the torques of bothof the motors to lower the bucket, and means responsive in all loweringoperating positions of said drum controller for automaticallymaintaining the bucket open throughout its downward travel andcomprising electroresponsive means for controlling the clutch to couplethe motors to one another thereby automatically to afford speed matchingof the holding andclosing lines.

9. The invention defined in claim 8, together with a dig switch, controlmeans responsive to concurrent operation of said dig switch and settingof said drum controllerto said hoisting operating positions forcontrolling the clutch to effect declutchingv of the motors and foroperating the closing line motor to close the bucket and for energizingthe holding line motor to maintain the holding lines taut, and controlmeans responsive to restoration of said dig switch to effectacceleration of both motors to hoist the bucket.

l0. The invention defined in claim 8, together with a load loweringswitch, control means responsive to concurrent operation of said loadlowering switch and setting of said drum controller in a loweringoperating position for controlling said electroresponsive means toprevent clutching of the motors and for energizing the holding linemotor to provide a small countertorque, and control means alsoresponsive'to said concurrent operation for energizing the closing linemotor to provide a relatively larger countertorque to maintain thebucket closed, the weight of the loaded bucket being greater than thesum of said countertorques to afford lowering of the loaded bucket.

ll. The invention defined in claim 8, together with a dump switch, andcontrol means responsive to concurrent operation of said dump switch andsetting of said drum controller to a lowering operating position forcontrolling said electroresponsive means to prevent clutching of themotors and for braking the holding line motor and operating the closingline motor to open the bucket thereby to dump the load.

12. In an electrical system for controlling the holding and closinglines of a two-motor buckethoist, a drum controller having a central offposition and a plurality of hoisting operating positions operable whensaid controller is rotated in one direction to progressively vary thehoisting speed of the bucket and a plurality of lowering operatingpositions operable when said controller is rotated in the oppositedirection to progressively vary the lowering speed of the bucket, and acontrol system for the holding line and closing line motors comprisingmeans responsive to setting of said drum controller in Aselectedhoisting operating positions for energizing both the holding line motorand the closing line motor in the hoisting direction and for adjustablycontrolling the speeds of both of the motors to hoist the bucket, andmeans responsive to setting of said drum controller in selected loweringoperating positions for energizing the holding line motor in thehoisting direction and the closing line motor in the lowering directionand for adjustably controlling the respective hoisting and loweringtorques of the motors to lower the bucket.

13. The invention defined in claim l2, together with means responsive tosetting of said drum controller in a maximum speed lowering operatingposition for decreasing the hoisting torque of the holding line motor asubstantial amount and for reversing the energization of the closingline motor to the hoisting direction and for controlling the closingline motor to develop a small amount of hoisting torque thereby toafford controlled acceleration of the bucket in the lowering direction.

emanan '"1'9 14. In a system for controlling the holdingline v'and'closing line motors of a plural-motor bucket hoist hav# ing anelectroresponsive clutch which'is operable to couple the motors forrotation in unison, control means for the motors comprising a singlemaster switch having a plurality of hoisting operating .positions yforcontrolling hoisting of the bucket at a plurality. of speed points and aplurality of lowering operating positions for con? trolling lowering ofthe bucket at a plurality of -speed points, means responsive to settingof said, master switch in selected lowering operating positions forenergizing' the'- holding line motor for hoisting 4at -a`torque-'substantially sufficient to balance the load; means responsiveto setting of said master switch in said lowering operating positionsfor effecting engagement ofthe 'clutch automatically to alford relativecontrol of the holding and closing lines in all lowering speed points,and means lll responsive to setting .of said master switch in saidlowering operating positions for energizingthe closing line motor'fo'rlowering 'at'adjstable' torque to maintainthe bucket open; and toIafford'.,controlledv speed lowering 'ofV theopen bucket.. .1.7L 'j 'figrfefaeeictea 11a the me of this patent l UNITED STATES PATENTS 2,671,567l Ready] Mar-9, 1954

